A conventional communications system generally includes one or more Layers or an Open Systems Interconnection (OSI) reference model. These layers include the Physical (PHY) Layer, the Medium Access Control (MAC) Layer which is a sublayer of the Data Link (DL) Layer, the Network (NET) Layer, the Transport Layer, the Session Layer, the Presentation Layer, and the Application Layer. A Protocol Reference Model (PRM) defines the system architecture including its fundamental building blocks as to how they are organized in a system and how they interact with each other.
A PRM usually consists of a Data Plane and a Management Plane. The Data Plane typically includes the functionalities defined in the OSI model. The Management Plane ensures exchange of management messages between various layers, and between the layers and the Station Management Entity (SME). SME is generally the substrate or the platform on which the communications system resides. Sometimes a device or a system consisting of the PHY, MAC and NET layers may be a part of a network of similar systems and interfacing between these entities may be required for the management and control purposes. Hence, a Network Control and Management System (NCMS) can be introduced. Introduction of an NCMS allows the general device architecture and its PHY/MAC functionalities to be independent of the network architecture, the transport network, the protocols used at the backend, hence allowing for a greater flexibility. The PHY and MAC Layers may interact with each other directly or through a Service Access Point (SAP). An SAP is a location at which one layer of the stack can request services from the other layer.
Conventional PRMs describing communications systems do not effectively account for the fact that the spectrum availability can be dynamic and unevenly distributed, i.e., some portions of the spectrum (channels) can be occupied by users in an area while others can be available for transmission, and this availability can vary in time.